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Cracked heat X ????

A cracked heat exchanger can be a bad situation. But with the newer furnaces that are essentially negative pressure, is there any harm? Today I found a heat exchanger, 16 years old, very rusty on the inside with seems that are 1/8 to 1/4 inch separated. No indication of a crack, but it made me nervous just looking at it. I brought the customer down to the furnace and explained that although I could not find a definitive crack, my gut feeling is that if I pulled the furnace out, I would find one. I used the bore scope and could see signs overheating. I red tagged it.
Questions. How far do you go to find a crack if you suspect one? What do you let go?

Id look at it if it were my own. The risk of running it would be too dangerous and i would tell the customer that. Its all about safety and my family comes first. I always go with my gut feeling. Sometimes the naked eye can't see everything but your gut instinct is usually right.

Furnaces have all ways been in a negative pressure... It's not co spilling out of a crack that should worry you. It's flue gases backing up due to air being Pulled in brought the failure causing high levels of co or flame roll out. According to the AGA....ANY failure is well enough to red tag a furnace

Furnaces have all ways been in a negative pressure... It's not co spilling out of a crack that should worry you. It's flue gases backing up due to air being Pulled in brought the failure causing high levels of co or flame roll out. According to the AGA....ANY failure is well enough to red tag a furnace

A rusted heat exchanger is not a failure if there is no "visible crack or hole".

I like to poke at rusty heat exhangers with a screw driver in a few spots, if it is copmpromised you will usually find out much quicker than taking it out. If I don't put a hole in it and I still am uncertain I will explain to the customer and let them decide if they want to pay me to take it apart and stress the safety factor.

I like to poke at rusty heat exhangers with a screw driver in a few spots, if it is copmpromised you will usually find out much quicker than taking it out. If I don't put a hole in it and I still am uncertain I will explain to the customer and let them decide if they want to pay me to take it apart and stress the safety factor.

Just don't let the homeowner see you jabbing their hx with your screwdriver!! LOL

These are good posts. Now you should also possibly consult with Jim Davis at NCI. He is the leading furnace expert in the industry.
Also if you use a combustion analyzer you will find that with a properly combusting furnace there is a very low risk of CO going into the home from a crack. But a low level CO monitor is a lifesaving investment for the H.O.

A cracked heat exchanger can be a bad situation. But with the newer furnaces that are essentially negative pressure, is there any harm? Today I found a heat exchanger, 16 years old, very rusty on the inside with seems that are 1/8 to 1/4 inch separated. No indication of a crack, but it made me nervous just looking at it. I brought the customer down to the furnace and explained that although I could not find a definitive crack, my gut feeling is that if I pulled the furnace out, I would find one. I used the bore scope and could see signs overheating. I red tagged it.
Questions. How far do you go to find a crack if you suspect one? What do you let go?

I understand what you mean about gut feelings on whether a furnace is safe or not but if you go by gut feelings and not evidence or CO readings than your relying on speculation and fear that you might have instilled to the unknowing homeowner. Just my opinion .